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The role of the intra-daily SST variability in the Indian monsoon variability and monsoon-ENSO–IOD relationships in a global coupled model

The role of the intra-daily SST variability in the Indian monsoon variability and monsoon-ENSO–IOD relationships in a global coupled model
The role of the intra-daily SST variability in the Indian monsoon variability and monsoon-ENSO–IOD relationships in a global coupled model
The impact of diurnal SST coupling and vertical oceanic resolution on the simulation of the Indian Summer Monsoon (ISM) and its relationships with El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) events are studied through the analysis of four integrations of a high resolution Coupled General Circulation Model (CGCM), but with different configurations. The only differences between the four integrations are the frequency of coupling between the ocean and atmosphere for the Sea Surface Temperature (SST) parameter (2 vs. 24 h coupling) and/or the vertical oceanic resolution (31 vs. 301 levels) in the CGCM. Although the summer mean tropical climate is reasonably well captured with all the configurations of the CGCM and is not significantly modified by changing the frequency of SST coupling from once to twelve per day, the ISM–ENSO teleconnections are rather poorly simulated in the two simulations in which SST is exchanged only once per day, independently of the vertical oceanic resolution used in the CGCM. Surprisingly, when 2 h SST coupling is implemented in the CGCM, the ISM–ENSO teleconnection is better simulated, particularly, the complex lead-lag relationships between the two phenomena, in which a weak ISM occurs during the developing phase of an El Niño event in the Pacific, are closely resembling the observed ones. Evidence is presented to show that these improvements are related to changes in the characteristics of the model’s El Niño which has a more realistic evolution in its developing and decaying phases, a stronger amplitude and a shift to lower frequencies when a 2-hourly SST coupling strategy is implemented without any significant changes in the basic state of the CGCM. As a consequence of these improvements in ENSO variability, the lead relationships between Indo-Pacific SSTs and ISM rainfall resemble the observed patterns more closely, the ISM–ENSO teleconnection is strengthened during boreal summer and ISM rainfall power spectrum is in better agreement with observations. On the other hand, the ISM–IOD teleconnection is sensitive to both SST coupling frequency and the vertical oceanic resolution, but increasing the vertical oceanic resolution is degrading the ISM–IOD teleconnection in the CGCM. These results highlight the need of a proper assessment of both temporal scale interactions and coupling strategies in order to improve current CGCMs. These results, which must be confirmed with other CGCMs, have also important implications for dynamical seasonal prediction systems or climate change projections of the monsoon.
Indian summer monsoon El Niño-Southern Oscillation Intra-daily SST variability Ocean–atmosphere interactions Coupled climate model
0930-7575
729-754
Terray, Pascal
7b49a30e-8d8f-42c2-84f6-1555ee4d72bd
Kamala, Kakitha
5f2ba603-e5e8-407b-951b-2e9e205029ba
Masson, Sébastien
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Madec, Gurvan
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Sahai, A.K.
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Luo, Jing-Jia
d17819b4-b29e-4b43-a81f-7465e3c8b628
Yamagata, Toshio
94509afb-faba-4a4b-9709-2d0dbb8f8635
Terray, Pascal
7b49a30e-8d8f-42c2-84f6-1555ee4d72bd
Kamala, Kakitha
5f2ba603-e5e8-407b-951b-2e9e205029ba
Masson, Sébastien
3c93954e-649f-478b-a35e-d06879fb5d12
Madec, Gurvan
ffb28deb-4bbd-4a4c-914f-492f813e4864
Sahai, A.K.
5a00c6e5-b859-482b-9dcd-f9b4f7c1ed9b
Luo, Jing-Jia
d17819b4-b29e-4b43-a81f-7465e3c8b628
Yamagata, Toshio
94509afb-faba-4a4b-9709-2d0dbb8f8635

Terray, Pascal, Kamala, Kakitha, Masson, Sébastien, Madec, Gurvan, Sahai, A.K., Luo, Jing-Jia and Yamagata, Toshio (2012) The role of the intra-daily SST variability in the Indian monsoon variability and monsoon-ENSO–IOD relationships in a global coupled model. Climate Dynamics, 39 (3-4), 729-754. (doi:10.1007/s00382-011-1240-9).

Record type: Article

Abstract

The impact of diurnal SST coupling and vertical oceanic resolution on the simulation of the Indian Summer Monsoon (ISM) and its relationships with El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) events are studied through the analysis of four integrations of a high resolution Coupled General Circulation Model (CGCM), but with different configurations. The only differences between the four integrations are the frequency of coupling between the ocean and atmosphere for the Sea Surface Temperature (SST) parameter (2 vs. 24 h coupling) and/or the vertical oceanic resolution (31 vs. 301 levels) in the CGCM. Although the summer mean tropical climate is reasonably well captured with all the configurations of the CGCM and is not significantly modified by changing the frequency of SST coupling from once to twelve per day, the ISM–ENSO teleconnections are rather poorly simulated in the two simulations in which SST is exchanged only once per day, independently of the vertical oceanic resolution used in the CGCM. Surprisingly, when 2 h SST coupling is implemented in the CGCM, the ISM–ENSO teleconnection is better simulated, particularly, the complex lead-lag relationships between the two phenomena, in which a weak ISM occurs during the developing phase of an El Niño event in the Pacific, are closely resembling the observed ones. Evidence is presented to show that these improvements are related to changes in the characteristics of the model’s El Niño which has a more realistic evolution in its developing and decaying phases, a stronger amplitude and a shift to lower frequencies when a 2-hourly SST coupling strategy is implemented without any significant changes in the basic state of the CGCM. As a consequence of these improvements in ENSO variability, the lead relationships between Indo-Pacific SSTs and ISM rainfall resemble the observed patterns more closely, the ISM–ENSO teleconnection is strengthened during boreal summer and ISM rainfall power spectrum is in better agreement with observations. On the other hand, the ISM–IOD teleconnection is sensitive to both SST coupling frequency and the vertical oceanic resolution, but increasing the vertical oceanic resolution is degrading the ISM–IOD teleconnection in the CGCM. These results highlight the need of a proper assessment of both temporal scale interactions and coupling strategies in order to improve current CGCMs. These results, which must be confirmed with other CGCMs, have also important implications for dynamical seasonal prediction systems or climate change projections of the monsoon.

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More information

Published date: August 2012
Keywords: Indian summer monsoon El Niño-Southern Oscillation Intra-daily SST variability Ocean–atmosphere interactions Coupled climate model
Organisations: Marine Systems Modelling

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Local EPrints ID: 351002
URI: https://eprints.soton.ac.uk/id/eprint/351002
ISSN: 0930-7575
PURE UUID: d10034c1-9651-4845-861a-1e5ce303ad19

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Date deposited: 12 Apr 2013 10:57
Last modified: 16 Jul 2019 21:37

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Contributors

Author: Pascal Terray
Author: Kakitha Kamala
Author: Sébastien Masson
Author: Gurvan Madec
Author: A.K. Sahai
Author: Jing-Jia Luo
Author: Toshio Yamagata

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